1. Field of the Invention
The present invention relates to rotary electric machines having a rotor core comprised of at least two or more core blocks. The core blocks are sequentially stacked in an axial direction of the rotor core. Each of the core blocks has a predetermined thickness. The assembly of the core blocks has a step skew structure in which the core blocks are shifted to each other in a circumferential direction by a skew having a predetermined phase angle of α (skew angle of α).
2. Description of the Related Art
A technique regarding a step skew structure is applied to rotary electric machines in order to obtain torque ripple reduction and magnetic noise reduction.
Such a step skew structure of the rotor core in the rotary electric machine is shown by a skew angle of α formed between the first core block and the second core block and a skew angle of α formed between the second core block and the third core block. In order to make a step skew structure in the rotor core, the first core block, the second core block and the third core block are sequentially stacked so that they are shifted to each other by the skew angle of α. Each of the first core block, the second core block and the third core block is comprised of a plurality of core sheets which are sequentially stacked, and a reference groove is formed on a central position P of a magnetic pole in the core sheets. In particular, the central position P of the magnetic pole is positioned on a half of the skew angle of α.
The second core block is obtained by reversing the first core block. The second core block is stacked on the third core block, and the first core block is stacked on the second core block. That is, in the rotor core, the first core block and the third core block are arranged in the same direction. On the other hand, a front part of the second core block is reversed in arrangement direction to the front part of the first core block and the front part of the third core block because the second core block is reversed in arrangement position to the first core block.
A burr is generated in each of the core sheets toward a punching direction by punching a steel sheet, and the burrs of the core sheets in each of the core blocks have the same direction. Further, the first core block and the second core block are stacked so that the direction of the burrs of the core sheets in the first core block is reversed in arrangement direction to the direction of the burrs of the core sheets in the second core blocks. The second core block and the third core blocks are stacked in the same arrangement direction. As a result, the burrs of the core sheets in the first core block and the burrs of the core sheets in the third core blocks have the same direction. On the other hand, the direction of the burrs of the core sheets in the second core blocks is different, i.e. reversed to the direction of the burrs of the core sheets in the first core block and the third core block. In other words, the burrs of the core sheets in the second core block are reversely arranged in direction to the burrs of the core sheets in the first core block and the third core block along an axial direction of the rotor core. This arrangement of the burrs generates a gap between the first core block and the second core block, and further generates a gap between the second core block and the third core block in the rotor core. A prior patent document, a Japanese patent laid open publication No. 2005-295744 discloses this conventional problem.
As previously described, such a gap is generated between the sequentially stacked core blocks in a step skew structure because the burrs of the core sheets in the first core block are reversed in arrangement direction to the burrs of the core sheets in the second core block, and the burrs of the core sheets in the second core block are reversed in arrangement direction to the burrs of the core sheets in the third core block. As a result, this causes a possibility of foreign matter entering the inside of the rotor core through the gap, and of separating fixing members which fix permanent magnets to the rotor core from the rotor core.